Synthesis and characterization of hydrogen-bonded assemblies of W6S8L6 clusters

Ligand-exchange reactions involving octahedral W6S8 clusters and a family of pyridine-based ligands (isonicotinic acid, isonicotinamide, 4-hydroxypyridine, 4-aminopyridine, 4-pyridineacetamide) have been explored with the goal of preparing compounds that crystallize in hydrogen-bonded arrays. Two new compounds, W6S8(4-pyridineacetamide)6.DMF.4-pyridineacetamide (1) and W6S8(4-aminopyridine)6.4DMF (2), were isolated and characterized by single-crystal X-ray diffraction. Both compounds crystallize in the P2(1)/c space group with a = 16.461(1), b = 33.08(2), c = 13.165(10) A, beta = 103.270(15) degrees for 1 and a = 13.8988(5), b = 13.2791(5), c = 15.6293(6) A, beta = 108.5410(10) degrees for 2. Each compound was further characterized by 1H NMR spectroscopy, elemental (CHN) analysis, and thermogravimetric analysis. Examination of the structures shows that 1 forms a three-dimensional hydrogen-bonded network in which each 4-pyridineacetamide ligand interacts with ligands on neighboring clusters or with the free ligand of crystallization. This is the first hydrogen-bonded network formed from W6S8 clusters. In 2, the amino groups act as hydrogen-bond donors toward DMF molecules of crystallization, but an extended array is not formed. In addition, the binding strengths of these pyridine-based ligands to the W6S8 cluster were studied through quantitative 1H NMR studies of ligand-exchange reactions. A qualitative relationship was found between ligand binding strengths and Hammett substituent constants for this group of ligands.     

Novel octahedral tungsten sulfidocyanide cluster anion [W6S8(CN)6]6-

Novel tungsten octahedral sulfidocyanide cluster compounds Na6[W6S8(CN)6].18DMSO 1 and K6[W6S8(CN)6] 2 have been synthesized and characterized by X-ray crystallography and NMR spectroscopy.     

簇合物Co6S8(PBun3)6的晶体结构及簇骼M6E8P6(E=S,Se,Te)的协同效应

簇骼为M6E8P6的六核簇合物的一个新成员--Co6S8(PBun3)6的合成和晶体结构表明,可能是由3个单核基元Co(PBun3)2S先组装成三核簇状基元化合物Co3(μ2-S)3(μ3-S)(PBun3)3,然后由2个这样的三核亚单元形成μ3-S桥生成该六核簇合物.讨论了簇骼为[M6E8P6]n(M=Fe,Mo,Co,Cr,W;E=S,Se,Te;n=-1,0,+1,+2,+3)的系列簇合物的分子内协同效应.     

New compounds in the cesium sulfobromide rhenium octahedral cluster chemistry: syntheses and crystal structures of Cs4Re6S8Br6 and Cs2Re6S8Br4

The exploration of the CsReSBr system, in order to identify new phases based on octahedral cluster anions, has produced single crystals of Cs₄Re₆S₈Br₆ (1) (trigonal, space group P-6c2, a=9.7825 (3) Å, c=18.7843 (5) Å, V=1556.77 (1) ų, Z=2, density=5.09 g cm⁻³, μ=36.07 mm⁻¹) and Cs₂Re₆S₈Br₄ (2) (monoclinic, space group P2₁/n, a=6.3664 (1) Å, b=18.4483 (4) Å, c=9.3094 (2) Å, β=104.2618 (8)°, V=1059.69 (4) ų, Z=2, density=6.14 g cm⁻³, μ=45.83 mm⁻¹). These two compounds have been obtained by high-temperature solid state route. Their structures have been solved and refined from single crystal X-ray diffraction data. The structure of Cs₄Re₆S₈Br₆ presents isolated anionic cluster units inscribed in a (Cs⁺)₁₂ cuboctahedron and the one of Cs₂Re₆S₈Br₄ exhibits ReS^i-a,a-iRe inter-unit bridges. The framework of the latter presents then a strongly 1-D character.     

Single-crystal structure of Cs2Re6S6Br8 rhenium thiobromide with acentric Re6 octahedral cluster units

Cs₂Re₆S₆Br₈ (trigonal, a = 10.001(5) Å, c = 14.676(5) Å) exhibits the same structure as Cs₂Mo₆Cl₈Br₆ and Cs₂Mo₆Br₁₄ that were described in a noncentro-and centrosymmetric space groups, respectively. The structure has been refined in P31c space group from a single crystal of actual composition Cs_1.95(1)Re₆S_5.82(3)Br_8.19(3) close to the cesium-rich end of the solid solution Cs₂Re₆S₆Br₈ — CsRe₆S₅Br₉. The centrosymmetry is respected by almost all the atoms of the asymmetric unit, but it is clearly broken by significant differences in the S/Br statistical distribution of the disordered “inner” ligands around the Re₆ cluster. Structural refinements from data collected at 100 K revealed that the Cs cation disorder is static. From the structure refinements, the stable isomers of the [Re₆S₆Br₂] and [Re₆S₅Br₃] cluster cores have been unambiguously determined.     

Self-asssembly of a molecular M8L12 cube having S6 symmetry

Reaction of the bis-bidentate ligand L1, having two bidentate pyrazolyl-pyridine termini, with Co(II) or Zn(II) results in formation of the complexes [M8(L1)12]X16 (X = perchlorate or tetrafluoroborate); [Zn8(L1)2](ClO4)16 has been structurally characterised and is a cube with a metal ion at each corner, a bridging ligand along each edge, and an anion in the central cavity.     

Synthesis and modeling study of (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy- 8-(1-decynyl)-benzolactam-V8 as protein kinase C modulators

[structures: see text] Both (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy-8-(1-decynyl)benzolactam-V8 were designed and synthesized as PKC modulators. Biological assays reveal the (6R)-ligand to be 20-fold more potent than its (6S)-counterpart in binding to PKC alpha.     

Synthesis and characterization of oxidized W(6)S(8)L(6) clusters

Cationic [W(6)S(8)L(6)]PF(6) (L = PEt(3) (3), 4-tert-butylpyridine (4)) clusters were successfully synthesized and isolated for the first time by reacting the corresponding neutral W(6)S(8)L(6) (L = PEt(3) (1), 4-tert-butylpyridine (2)) clusters with [Cp(2)Fe]PF(6) as the oxidant. The products 3 and 4 were characterized by NMR spectroscopy, mass spectroscopy, and X-ray crystallography (only for 3) and shown to be the desired oxidized W(6)S(8) clusters with a metal electron count of 19. Magnetic property studies showed that they are paramagnetic compounds with S = (1)/(2). Their chemical properties and stability are also reported. Crystal data for 3.2 THF: space group, R3 (No. 148); a = 13.91170(10) A; c = 32.4106(2) A; Z = 3.     

Total synthesis of (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A and (-)-(6S,7S,8S,9R,10S)- membrenone-B and structural assignment of membrenone-C

[reaction: see text] (-)-(6S,7S,8S,9R,10S,2'S)-Membrenone-A and (-)-(6S,7S,8S,9R,10S)-membrenone-B were prepared in 11 steps (3% and 2.4% overall yield, respectively). Key steps included a tin(II)-mediated aldol followed by a syn selective reduction, giving the C7-C9 stereocenters, a second chain extending aldol coupling, and a p-TsOH-promoted cyclization/dehydration giving the common gamma-dihydropyrone precursor. We have thus established that synthetic (-)-(6S,7S,8S,9R,10S,2'S)-membrenone-A, (-)-(6S,7S,8S,9R,10S)-membrenone-B, and (-)-(6S,7S,8S,9R,10S)-membrenone-C are the enantiomers of the natural products.